RESUMEN
Pregnancy is considered to be one of the physiological stressors. The stress hormone, cortisol is significantly involved in various events during periparturient period including initiation of parturition. The study was conducted to estimate the serum cortisol concentration in cows and the neonatal calves in order to correlate the effect of cortisol on certain haematological and biochemical parameters such as blood glucose level (BGL), total plasma protein (TPP), lymphocyte:neutrophil ratio and mitogen induced lymphocyte proliferative response. Blood samples were collected from six cows in four periods, namely., 3 days prior to parturition, on the day of parturition, and 7 days after parturition. Blood samples were also collected from neonatal calves in the period 0, 7 and 14 days of age. Calves above two months of age and non-pregnant dry cows were considered as the controls. The serum cortisol concentration in cows on the day of parturition was significantly higher (P < 0.01) than controls and the value in calves was also significantly higher (P < 0.01) at 0 day than their controls. On the day of parturition BGL level of the dam and calves were significantly higher (P < 0.01), whereas the proliferative response of lymphocytes to mitogen was significantly lower (P < 0.01) than controls. However TPP levels did not differ significantly. This confirmed that the dam at the time of parturition and neonatal calf before taking colostrum are under a high risk of infection because of the low profile of immune status. The lymphocyte:neutrophil ratio also justified the above suggestion.